Kombucha is a good replacement for soft drink and it's really easy to make at home. Get a big glass jar (I do mine in batches of about 4L/1 gallon). Boil your 4L of water in a big saucepan, add a cup of white sugar, and about 6 tea bags. After it's boiled take the tea bags out and let it cool to body temp. Add it to your big glass jar and add a starter scoby (they're like $10 on Amazon). After about 5-10 days you take the Kombucha out of the big jar and put it into small bottles, I use swing top beer bottles. Leave the scoby and a little bit of liquid in the jar for your next batch . You can add something to the bottles for flavour and secondary fermentation at this point, I use 50ml of cordial. Leave the bottles for a few days and then consume.

I have mine running perpetually and consume about one bottle a day. As soon as I bottle some I put more tea in the jar. It's costs maybe a dollar or two per batch.